Electromagnetically Induced Transparency
Daniel's description of how the beam of energy work is as follows:
The beam of energy, which is now acting on the metal of the door, is what you would call a frequency multiplier. The beam penetrates the metal and acts upon any light that reaches it in such a way that the frequency of the light is multiplied to that of the range between what you know as the "X-ray" and the "Cosmic Ray" spectrums. At these frequencies the waves pass through the metal quite readily. Then, when these waves leave the metal on the inside of the door, they again interact with the viewing beam, producing what you would call `beat' frequencies which are identical with the original frequencies of the light, so that while you are apparently seeing through the metal you are actually seeing a reproduction.
The author of this book ran the description above by a practicing physicist and she asked "Even though it is known that light will create beat frequencies with higher frequency EM waves, the problem is that once the resulting frequency passes into the compartment, how is it demodulated?" The light doesn't need to be demodulated because it only combines with the beam as it passed through the metal and once on the other side, continues on it's merry way as a separate wave. The light passes through the metal wall due to superposition with the "viewing" beam. Below is an analogy made up of two colored lights, the first red line is a red light and the other is green light. If you were to stand at point "A", both light beams would shine into your eye and you would see yellow. If you stood at point "B", all you would see green light.
In a similar way to the analogy, the outgoing "viewing" beam is the red line and at point "A" is the wall of the craft where the incoming light beams, "B" combines. Once on the other side of the wall and clear of the wall, the "B" light from outside will continue into the eye of the beholder without having to be demodulated. Even though the two frequencies of the "A" and "B" are far apart, they will still both combine under the principal of superposition. Even if the viewing beam works, the frequency of the original beam of energy from inside the ship will have to be high enough to penetrate metal. Such high frequency beams are dangerous to living thing and occupants inside the craft would have be careful about not standing in front of the beam.